Radiation-emitting semiconductor component and method for making same

ABSTRACT

A radiation-emitting semiconductor component having a semiconductor body ( 1 ), which has a radiation-generating active layer ( 9 ) and a p-conducting contact layer ( 2 ), which contains InGaN or AlInGaN and to which a contact metalization ( 3 ) is applied.

[0001] The invention describes a radiation-emitting semiconductor component according to the preamble of patent claim 1 and also a method for producing a radiation-emitting semiconductor component according to the preamble of patent claim 16.

[0002] Radiation-emitting semiconductor components of the type mentioned have a semiconductor body with a p-conducting and an n-conducting side, which are in each case connected to a contact area. The contact areas are generally formed as metal areas to which, by way of example, a wire connection can be connected or by which the semiconductor body can be mounted onto a chip pad. During operation, an operating current is impressed into the component via the wire connection or the chip pad. A highly doped contact layer, to which the contact area is applied in the form of a contact metalization, is usually provided in the semiconductor body.

[0003] In the case of semiconductor components based on GaN, AlGaN, InGaN and/or AlInGaN, which are referred to hereinafter as “GaN-based” for short, a p-GaN contact layer is often used on the p-conducting side of the semiconductor body. A comparatively high contact resistance occurs here upon the connection of the p-conducting contact layer and the contact metalization. The electrical power dropped across the contact resistance is converted into heat loss and is no longer available for the functional operation of the component, for example for generating radiation in the case of a radiation-emitting component. In the case of GaN-based components, the proportion of the power loss dropped across the contact resistance with respect to the total electrical power may amount to 50% or more. Furthermore, the resulting heat loss leads to heating of the component, the component being at risk of damage at excessively high temperatures. Therefore, it is desirable to keep the contact resistance as low as possible. This applies in particular to laser diode components which are operated with a high current and have a high thermal sensitivity. Thus, temperature changes may lead to instabilities in the laser mode and changes in the emission wavelength. Furthermore, the laser mirrors may be damaged by excessively high temperatures, which generally results in an irreversible total failure of the laser diode.

[0004] It is an object of the present invention to provide a radiation-emitting semiconductor component with an improved contact, which, in particular, has a low contact resistance. Furthermore, it is an object of the present invention to specify a method for producing a component with an improved contact.

[0005] This object is achieved by means of a radiation-emitting semiconductor component according to patent claim 1 and, respectively, a method according to patent claim 16. The dependent claims relate to advantageous developments of the invention.

[0006] The invention provides for the formation of a radiation-emitting semiconductor component having a semiconductor body, which has a radiation-generating active layer and a p-conducting contact layer with a contact metalization applied thereto, the contact layer containing InGaN or AlInGaN.

[0007] It has been shown, surprisingly, that the contact resistance is significantly lower in the case of a semiconductor component having an In-containing contact layer than in the case of a component having a p-GaN contact layer. The In content in the contact layer is preferably greater than 1 atomic % and preferably lies between about 1 atomic % and 9 atomic %, particularly preferably in a range of between 3 atomic % and 6 atomic %, in each case relative to the group III lattice sites, the limits of the range being included.

[0008] By way of example, magnesium or zinc may be used as p-type doping of the contact layer, an Mg doping having proved to be advantageous with regard to reducing the contact resistance. In particular, a higher Mg concentration can be formed in the case of the invention than in the case of a p-GaN layer according to the prior art.

[0009] In this case, it must be taken into account that the maximum Mg concentration is limited, inter alia, by self-compensation effects which predominate, starting from a certain concentration, in such a way that a further increase in the Mg concentration is not expedient since this does not effect a further increase in the charge carrier density. For p-GaN, this maximum concentration is about 5·10¹⁹ cm⁻³. In the case of the invention, by contrast, the Mg concentration can be increased to more than 2·10²⁰ cm⁻³.

[0010] As the contact metalization, a PdAu or NiAu layer is preferably formed on the contact layer. Other metals such as platinum, for example, are also suitable as the contact metalization. For a PdAu or NiAu contact metalization, it is preferably the case that firstly a Pd or Ni layer, respectively, is vapor-deposited onto the contact layer and an Au layer is vapor-deposited onto said Pd or Ni layer. The metal layers are subsequently alloyed. The alloying of the metal layers is typically effected at temperatures of between 200° C. and 1000° C., preferably between 200° C. and 800° C., since the risk of damage to the semiconductor layers increases at temperatures above 800° C.

[0011] Generally, it has proved to be advantageous, surprisingly, to form the p-conducting contact layer in such a way that it has a defect density that is as large as possible. In this case, defects are to be understood to be, in particular, threadlike defects such as threadlike dislocations. The defect density of p-GaN contact layers according to the prior art is typically of the order of magnitude of 10⁹ cm⁻². It has been shown in the case of the invention that higher defect densities, for example of the order of magnitude of 5·10⁹ cm⁻² to 5·10¹⁰ cm⁻², lead to a lower contact resistance.

[0012] In the case of a method according to the invention for producing a radiation-emitting component, firstly a p-conducting In-containing GaN-based contact layer is applied on a semiconductor body, in which an active radiation-generating layer is formed, and a contact metalization is subsequently formed on said contact layer.

[0013] The p-conducting contact layer is preferably grown epitaxially. In this case, it has proved to be advantageous to carry out the epitaxy at a comparatively low temperature. p-GaN contact layers are usually grown at about 1000° C. according to the prior art. It has been shown that the contact resistance can be lowered by growing the contact layer at a lower temperature, for example at 800° C. or 770° C. Preferably, in the case of the invention, the contact layer is deposited epitaxially at a temperature in the range of between 700° C. and 950° C., particularly preferably between 750° C. and 850° C.

[0014] Furthermore, in order to reduce the contact resistance, it is advantageous to use nitrogen as a carrier gas during the epitaxy of the contact layer.

[0015] Further features, advantages and expediences of the invention are explained in more detail below using four exemplary embodiments in conjunction with FIGS. 1 and 4.

[0016] In the Figures:

[0017]FIG. 1 shows a diagrammatic sectional illustration of a first exemplary embodiment of a semiconductor component according to the invention,

[0018]FIG. 2 shows a diagrammatic sectional illustration of a second exemplary embodiment of a semiconductor component according to the invention,

[0019]FIG. 3 shows a diagrammatic illustration of an I/U characteristic curve of a third exemplary embodiment of a semiconductor component according to the invention in comparison with an I/U characteristic curve of a component according to the prior art, and

[0020]FIG. 4 shows a diagrammatic illustration of an I/U characteristic curve of a fourth exemplary embodiment of a semiconductor component according to the invention in comparison with an I/U characteristic curve of a component according to the prior art.

[0021] Identical or identically acting elements are provided with the same reference symbols in the Figures.

[0022] The semiconductor component illustrated in FIG. 1 has a GaN-based semiconductor body 1 with a p-conducting and an n-conducting side and also an active radiation-generating layer 9. A contact metalization 3 is applied on a main area on the p-conducting side, and a further contact metalization 4 is applied as counter-contact oppositely on a main area of the n-conducting side. In the case of GaN-based semiconductor bodies, the n-side contact resistance is generally significantly lower than the p-side contact resistance. Since the contact resistances are connected in series via the intervening semiconductor body, it is necessary, in particular, in order to lower the total contact resistance, to reduce the contact resistance on the p-conducting side.

[0023] For this purpose, in the case of the invention, a p-conducting InGaN or AlInGaN contact layer 2 bounding the semiconductor body 1 is formed on the p-conducting side of the semiconductor body. The In content preferably lies between 1 atomic % and 9 atomic %, particularly preferably between 3 atomic % and 6 atomic %, in each case relative to the group III lattice sites. By way of example, a PdAu alloy serves as the contact metalization. For this purpose, firstly a Pd layer is vapor-deposited onto the p-conducting InGaN or AlInGaN contact layer 2 and an Au layer is vapor-deposited onto said Pd layer and said layers are subsequently converted into a PdAu alloy at an elevated temperature. The p-side contact resistance is significantly lower in the case of this exemplary embodiment than in the case of a corresponding arrangement of a contact metalization on an indium-free p-GaN contact layer according to the prior art.

[0024] In order to decrease the contact resistance further, it is advantageous during the production of the semiconductor body by means of an epitaxy method to grow the contact layer at a comparatively low temperature of about 800° C. and/or to use nitrogen as a carrier gas during the deposition of the p-conducting contact layer. This produces a comparatively high density of defects, in particular threadlike dislocations, in the p-conducting contact layer, which is typically 10¹⁰ cm⁻² and is thus about a factor of 10 greater than the defect density of a conventional contact layer. This brings about an advantageous decrease in the contact resistance.

[0025]FIG. 2 shows a further exemplary embodiment of a semiconductor component according to the invention. In this case, the semiconductor body is structured as a semiconductor laser. On a substrate 5, for example an SiC substrate, there are applied an n-conducting first cladding layer 7, an n-conducting first waveguide layer 8, an active layer 9, a p-conducting second waveguide layer 10, a p-conducting second cladding layer 11 and a p-conducting InGaN contact layer 2. The p-conducting contact layer 2 is provided with a contact metalization 3. A buffer layer 6 is preferably formed between the substrate 5 and the first cladding layer 7, said buffer layer serving to compensate for the different lattice constants of the substrate and the semiconductor layers of the semiconductor laser structure.

[0026] In the exemplary embodiment, the substrate is understood as part of the semiconductor body, in which case the substrate itself, in contrast to the layers applied thereon, may also be composed of a material which is not a semiconductor. Thus, the semiconductor body may also contain a different substrate, such as a sapphire substrate, for example. However, such an electrically nonconductive substrate requires an altered arrangement of the counter-contact 4 (not illustrated).

[0027] By way of example, the first and second cladding layers may comprise AlGaN, and the first and second waveguide layers may comprise GaN. In order to form the n-type conduction, the first cladding layer 7 and the first waveguide layer 8 are Si-doped. The p-type conduction in the second cladding layer 11 and the second waveguide layer 10 is achieved by Mg doping.

[0028] The active layer 9 comprises a plurality of quantum films 12, which may be formed for example from a sequence of thin InGaN and GaN layers. More widely, the quantum films may also contain AlGaN or AlInGaN.

[0029] In particular, a PdAu alloy or an NiAu alloy is again suitable as the contact metalization, which alloy may be produced as in the case of the first exemplary embodiment. However, other contact metalizations, for example a Pt layer, may also be used in the case of the invention.

[0030]FIG. 3 illustrates one I/U characteristic curve of an exemplary embodiment of a component according to the invention in comparison with an I/U characteristic curve of a component according to the prior art. The voltage U across the component is plotted as a function of a current I impressed into the component. The line 13 or the associated measurement points represent the measurement results of the component according to the invention, and the measurement points 14 represent the corresponding results according to the prior art.

[0031] In this case, the structure of the components essentially corresponds to FIG. 2. Specifically, a 100 nm thick buffer layer 6 made of Al_(0.2)Ga_(0.8)N, a 500 nm thick first cladding layer 7 made of Al_(0.2)Ga_(0.8)N, a 100 nm thick first waveguide layer 8 made of GaN, an active layer, a 126 nm thick second waveguide layer 10 made of GaN and a 400 nm thick second cladding layer 11 made of Al_(0.1)Ga_(0.9)N were applied to an SiC substrate 5. The buffer layer 5, the first cladding layer 6 and the first waveguide layer 7 are Si-doped and correspondingly n-conducting, and the second waveguide layer 10 and the second cladding layer 11 are Mg-doped and therefore p-conducting.

[0032] The active layer 9 comprises a quantum film structure which specifically comprises, in the direction of the contact layer, a 3 nm thick InGaN layer, a 5 nm thick GaN barrier layer, a 3 nm thick InGaN layer, a 5 nm thick GaN barrier layer, a 3 nm thick InGaN layer and a 15 nm thick, Mg-doped Al_(0.09)Ga_(0.91)N barrier layer.

[0033] In the case of the component according to the invention, a 100 nm thick, Mg-doped contact layer 2 made of InGaN with an indium proportion of 3% is deposited onto the second cladding layer 11, said layer having been grown epitaxially at a comparatively low temperature of 800° C. In the case of the component according to the prior art, for comparison, a 100 nm thick p-GaN contact layer was applied epitaxially at 1000° C. As the contact metalization, a Pd layer having a thickness of 50 nm and an Au layer having a thickness of 100 nm were in each case vapor-deposited onto the contact layer 2 and subsequently alloyed.

[0034] The contacts were embodied as so-called CTLM contacts (CTLM: circular transmission line method) in order to measure the I/U characteristic curve. The I/U characteristic curve of a circular contact with a diameter of 310 μm with respect to a large-area contact was measured, the contacts being separated by a 45 μm wide ring.

[0035] As emerges from FIG. 3, the I/U characteristic curve is significantly more linear and more weakly curved in the case of the component according to the invention than in the case of the component according to the prior art. The contact in the case of the component according to the invention therefore advantageously has a better ohmic behavior. Moreover, particularly in the vicinity of the zero point (I=0A, U=0V), both the absolute resistance U/I and the differential resistance dU/dI are lower than in the case of the component according to the prior art.

[0036]FIG. 4 illustrates the I/U characteristic curves of similar components. In contrast to the previously described exemplary embodiment, a contact metalization 3 having a lateral size of 750 μm×50 μm is applied in each case on the contact layer 2. On the side remote from the semiconductor layer sequence, the substrate 5 is provided with a counter-contact 4 over the whole area, and the lateral sample size is typically 3 mm×3 mm. The rest of the construction and, in particular, the composition and production of the contact layer correspond to the previously described exemplary embodiment.

[0037] The associated I/U characteristic curves are illustrated in FIG. 4. Line 15 represents the measured values for the component according to the invention with an InGaN contact layer, and line 16 represents the measured values for the component according to the prior art with a p-GaN contact layer. Both characteristic curves have a steep rise in the vicinity of the zero point, followed by a significantly shallower profile as the current rises. In this second, shallower section, the voltage U that is present with respect to a specific current I is significantly lower in the case of the component according to the invention than in the case of the component according to the prior art. Consequently, the component according to the invention has a significantly lower absolute resistance U/I in this region.

[0038] The explanation of the invention on the basis of the exemplary embodiments described does not, of course, constitute a restriction of the invention thereto. The invention relates to radiation-emitting components such as, for example, light-emitting diodes (LEDs) and laser diodes, but is generally also suitable for other GaN-based components. 

1. A radiation-emitting semiconductor component having a semiconductor body (1), which has a radiation-generating active layer (9) and a p-conducting contact layer (2), a contact metalization (3) being applied to the p-conducting contact layer (2), characterized in that the contact layer (2) contains In_(x)Ga_(1-x)N, 0<x≦1 or Al_(y)In_(x)Ga_(1-x-y)N, 0<x≦1, 0≦y<1, 0<x+y≦1.
 2. The radiation-emitting semiconductor component as claimed in claim 1, characterized in that the contact layer (2) is doped with magnesium.
 3. The radiation-emitting semiconductor component as claimed in claim 1, wherein the proportion of indium in the contact layer (2) is greater than or equal to 1 atomic % relative to the group III lattice sites.
 4. The radiation-emitting semiconductor component as claimed in claim 1, wherein the contact metalization (3) contains at least one of the elements Pd, Ni, Au or Pt or an alloy of at least two of said elements.
 5. The radiation-emitting semiconductor component as claimed in claim 1, wherein the thickness of the contact layer (2) lies between 0.01 μm and 1.0 μm, inclusive.
 6. The radiation-emitting semiconductor component as claimed in claim 1, wherein the semiconductor body (1) has a semiconductor layer sequence in which an n-conducting first cladding layer (7), an n-conducting first waveguide layer (8), an active layer (9), a p-conducting second waveguide layer (10), a p-conducting second cladding layer (11) and the contact layer (2) are arranged in order in the direction of the contact metalization (3).
 7. The radiation-emitting semiconductor component as claimed in claim 6, wherein the first cladding layer (7) contains n-AlGaN and the second cladding layer contains p-AlGaN (11).
 8. The radiation-emitting semiconductor component as claimed in claim 6, wherein the first waveguide layer (8) contains n-GaN and the second waveguide layer (10) contains p-GaN.
 9. The radiation-emitting semiconductor component as claimed in claim 1, wherein the active layer (9) comprises at least one quantum film (12) containing In_(x)Ga_(1-x)N, 0≦x≦1 or Al_(y)In_(x)Ga_(1-x-y)N, 0≦x≦1, 0≦y≦1, 0≦x+y≦1.
 10. The radiation-emitting semiconductor component as claimed in claim 1, wherein the contact layer (2) has a defect density which is greater than or equal to 5·10⁹ cm⁻².
 11. The radiation-emitting semiconductor component as claimed in claim 1, wherein the semiconductor body (1) has a substrate (5) on the side remote from the contact layer (2).
 12. The radiation-emitting semiconductor component as claimed in claim 11, wherein the substrate (5) contains SiC.
 13. The radiation-emitting semiconductor component as claimed in claim 11, wherein the substrate (5) contains sapphire.
 14. The radiation-emitting semiconductor component as claimed in claim 11, wherein the semiconductor body contains a buffer layer (6) adjoining the substrate (5).
 15. The radiation-emitting semiconductor component as claimed in claim 1, wherein the component is a luminescence diode, in particular a laser diode or an LED.
 16. A method for producing a radiation-emitting semiconductor component, comprising: a) providing a semiconductor surface, b) applying a p-conducting contact layer (2), which contains In_(x)Ga_(1-x)N, 0<x≦1 or Al_(y)In_(x)Ga_(1-x-y)N, 0<x≦1, 0<y≦1, 0<x+y≦1, to the semiconductor surface, and c) applying a contact metalization (3) to the p-conducting contact layer (2).
 17. The method as claimed in claim 16, wherein said step of providing a semiconductor surface comprises epitaxially depositing a plurality of semiconductor layers on a substrate (5), so that a surface of the semiconductor layer deposited last forms said semiconductor surface.
 18. The method as claimed in claim 16 wherein in step b), the p-conducting contact layer (2) is deposited epitaxially on said semiconductor surface.
 19. The method as claimed in claim 18, wherein in step b), the contact layer (2) is deposited at a temperature of between 700° C. and 1000° C.
 20. The method as claimed in claim 18 wherein nitrogen is used as carrier gas during the deposition of the contact layer (2).
 21. The radiation-emitting semiconductor component as claimed in claim 3, wherein the proportion of indium in the contact layer (2) is between 1 atomic % and 9 atomic %, inclusive, relative to the group III lattice sites.
 22. The radiation-emitting semiconductor component as claimed in claim 3, wherein the proportion of indium in the contact layer (2) is between 3 atomic % and 6 atomic %, inclusive, relative to the group III lattice sites.
 23. The radiation-emitting semiconductor component as claimed in claim 5, wherein the thickness of said contact layer (2) is between 0.1 μm and 0.2 μm, inclusive.
 24. The radiation-emitting semiconductor component as claimed in claim 10, wherein the contact layer (2) has a defect density which is greater than or equal to 1.10¹⁰ cm⁻².
 25. The method as claimed in claim 19, wherein in step b), the contact layer (2) is deposited at a temperature of between 750° C. and 850° C. 